1. Field of the Invention
The present invention relates to methods for compensating for variations in a manufacturing process. In particular, the present invention relates to applying such methods to optical instruments.
2. Discussion of the Related Art
The capsule camera has proved to be an effective minimally-invasive way for examining the gastrointestinal (GI) tract. One example of a swallowable capsule camera is described in the U.S. Pat. No. 5,604,531, issued to the Ministry of Defense, State of Israel. A number of patents assigned to Given Imaging describe in greater detail a capsule camera system which uses a transmitter to send images captured by the camera to an external receiver. Other capsule camera examples include U.S. Pat. Nos. 6,709,387 and 6,428,469. There are also other patents to the Olympus Corporation regarding capsule cameras. For example, U.S. Pat. No. 4,278,077 discloses a film camera in a capsule designed for the stomach. U.S. Pat. No. 6,939,292 discloses a capsule camera with a buffering memory and a transmitter. U.S. Pat. No. 6,800,060 discloses a capsule camera which stores image data in an atomic resolution storage (ARS) device.
Various advancements in electronics may now be incorporated into the capsule camera. For example, an LED provides a compact and low-power lighting source. CMOS image sensors reduce the component count and power. The further miniaturizing of integrated circuit geometry allows SOC (system-on-a-chip) techniques to be used, which reduce the size and power of the capsule camera. However, size reduction pushes the limits of manufacturing tolerances. For example, manufacturing processes for semiconductor image sensors inherently include not only lot-to-lot, wafer-to-wafer, and die-to-die variations, but also pixel-to-pixel variations within a die. Even the analog circuits sensing the charge stored in a cell to provide digital image data vary from location to location within a die. In addition, LEDs are known for variations in their light spectrum and intensity. Also, because the center of a lens passes light better than at the edge, a higher intensity results in the center of the image than at the edges. There are also variations from lens to lens, even if the lenses are fabricated from the same mold.
Another example results from the fact that illumination sources in a capsule camera illuminate objects only a few centimeters away, the objects receive non-uniform light intensities. Moreover, the transparent window provided in the capsule housing for the LED light to pass through is not perfectly transparent. Thus, when the light sources in the capsule (e.g., LEDs) are turned on, the transparent window reflects some of the light within the camera's field of view back to the light sources and the image sensor.
As the capsule camera is intended to allow a physician to examine the inside of a patient's GI tract, its accuracy and image quality are of paramount concern.